Direct Liquid Phase Hydroxylation of Benzene to Phenol over Iron-Containing Mordenite Catalysts: Combined DLS–EPR Study and Thermodynamic–Stability Analysis

Direct hydroxylation of benzene to phenol using hydrogen peroxide is a cornerstone of sustainable green chemistry. This paper presents the results of a stability study of an iron-containing mordenite catalyst in the liquid-phase hydroxylation of benzene to phenol with a 30% aqueous hydrogen peroxide solution. The study utilizes a combination of catalytic activity measurements, dynamic light scattering (DLS), and electron paramagnetic resonance (EPR) spectra. The system is initially shown to exhibit high phenol selectivity; however, over time, DLS measurements indicate aggregation of the catalyst particles with an increase in the average particle diameter from 1.8 to 2.6 μm and the formation of byproducts–dihydroxybenzenes. Iron is present predominantly as magnetite nanoparticles (Fe3O4) ~10 nm in diameter, stabilized on the outer surface of mordenite, with minor leaching (